Fluid heater unit



June 10, 1952 Filed Dec. 18, 1946 e. A. TAYLOR FLUID HEATER UNI T 2 SHEETS-SHEET l F; INVENTOR 9 George A. Taylor June 10, 1952 G. A. TAYLOR FLUID HEATER UNIT Filed Dec. 18, 1946 2 SHEETS-SHEET 2 N 9* N R mw m m w v I ug. s v

.8 mm x l WIWW HP HH I I HI I IHH I' I I IN I IMV .\\w R mm? M Q I w 3 mm? m w Mm Qm mm Patented June 10, 1952 .FLUID HEATER UNIT George A. Taylor, East Orange,

The Babcock & Wilcox Company,

N. J assignor to .Rockleigh,

N. J., a corporation of New Jersey Application December 18, 1946, Serial No. 716,999

.9 Claims.

The invention herein disclosed relates to the construction and operation of a tubular heat exchanger involving particularly the delivery of a gaseous medium thereto. My invention is especially useful in its application to air heater operation wherein the heating medium may be, for example, the hot gaseous products of combustion from a boiler furnace, and the medium to be heated, the major portion of the air required for combustionof fuel within such a furnace.

In modern high capacity boiler installations operating, for example, at vapor generating capacities of 500,000or more pounds of steam per hour, the rate at which heated combustion air must be supplied is often approximately equal to the rate of steam flow. It is also usually required to heat the combustion air to relatively high temperatures, of 500 F. or more, making it necessary to provide an air heater having a considerable area of heat transfer surface to the meet the conditions of air flow rate and temperature.

In a conventional form of air heater wherein the heat transfer elements are -in the form of tubes arranged in a ban-k from one end of the air heater to the other, the air to be heated may be directed over the outer surfaces of the tubes, and a fluid heating medium, such as hot combustion gases, directed through the tubes,

the air being suitably directed in series over successive lengths of tubes in a plurality of transverse passes. Where a large sized large capacity cross flow air heater is involved, the inlet for cold air generally extendsthroughout the full width of the tube bank which in some instances may involve a cold air inlet of at least 40 feet in width, the height of the. inlettbeing substantially equal to the height of the first or inlet pass across the tubes and together defining a fiow area comparable to the high rate of air flow required.

Assuming the gas and air to flow through the air heater in generally counterfiow relation, it is known that those portions of the tube lengths in the air inlet pass, and-particularly those vadjacent the entrance to lthe pass, are subject to fairly rapid corrosion unless operated at temperatures high enough to prevent athe condensation of va'pors passing therethrough. This problem is often met by bypassing a portion of the incoming air around at least la portion of the heat transfersurface and thereby reduce the cooling efiect'on'the. gas discharge end portions of the tubes. However, such bypassingcof vair .2 reduces the rate of air flow throughout the entire air heater and for a given design of boiler unit may result in an appreciable decrease in overall efiiciency due to the accompanying higher gas outlet temperatures.

The corrosive effect mentioned is generally the result of the condensation of water vapor carried by the heating gases flowing in contact with the metallic heat transfer surfaces, combined with the presence of a gaseous constituent such as sulphur dioxide resulting from combustion of the fuel by which the gases are generated. The condensation is promoted when the metal of the tubes, for example, adjacent the cooler gas exit end, is compelled to operate at relatively low temperatures due to the continuous contact .of cold inlet air with one surface of the element and the continuous contact of cooled gases with another surface. Condensation of the water vapor also maintains the heat transfer surfaces in a moist condition which is conducive to the collection of dust particles on the surfaces and a consequent decrease in heat transfer ,efiiciency. When the heat transfer elements are tubular members and the particlecarrying gases are directed therethrough, such members eventually become plugged and their elfectiveness as heat transfer elements completely nullified.

In .a tubular air heater adapted for high capacity operation, it is often both convenient .and necessary to employ more than one forced draft fan for supplying air to the heater at the required high rate of flow. The cold air inlet is consequently of large area and in accordance with current practice is generally many times wider in one direction than in another. This presents a problemof proper distribution of air over the gas exit ends of the tubes and unless substantially uniform distribution is effected the result is a chilling of certain tubes adjacent the cold air inlet with a consequent decrease of heat transfer eificiency and possible corrosion. Non-uniform air delivery also has an adverse effect on the overall average of heat transfer throughout the tube bank adjacent the gas outlet end and results in reduced overall ,efiiciency of the air heater surface.

,An object of my invention therefore in fluid heater operation is to maintain the heat transfer efficiency of metallic elements through the alleviation of conditions conductive to deterioration thereof.

Another objectis to maintainsubstantially the sameextent of delivery of;a gaseous fluid to heat transfer elements utilizing separately operable fluid delivery means.

An additional object is to maintain high capacity operation of a tubular air heater utilizing two forced draft air delivery fans while effecting substantially the same distribution of air by each fan to heat transfer elements adjacent the air heater air inlet.

A further object is to effect distribution of inlet air throughout a row of air heater tubes by delivering the air thereto in one or more obliquely directed streams.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is an elevational view mainly in section illustrating an embodiment of my invention; and,

Fig. 2 is a plan view, partly in section, of the apparatus shown in Fig. 1.

As illustrated, my invention is shown in connection with an air heater 4 of a tubular type having an outer enclosing casing 5 within which are disposed closely spaced upright tubes 3 arranged in a bank of horizontally rectangular cross-section spaced from opposite side walls of the casing, as seen in Fig. 2, the tubes 6 being connected at opposite ends to upper and lower tube sheets i and 8 respectively. The air heater is especially adapted for association with a high capacity vapor generating unit of the construction shown, for example, in the copending application of Arthur E. Raynor, Serial No. 638,941,

filed January 4, 1946, now Patent No. 2,512,677,

a flue 9 serving to conduct hot heating gases from the gas outlet of such a unit and to direct the gases to the air heater gas inlet l2 adjacent the lower tube sheet 8, the gases passing upwardly through the tubes 6 and being discharged there- .from through a flue l3 defining the air heater gas outlet l4 adjacent the upper tube sheet 1.

Air to be heated is directed into the casing 5 through a rectangular air inlet opening l5 in an upper portion of the front wall l6 of the casing, and the heated air discharged through a similar rectangular air outlet opening I! in a lower portion of the same wall. The air is directed across the bank of tubes 6 by vertically spaced horizontally disposed bafiles l8, l9 and 29 defining serially connected transverse air flow passes 23, 24 and 25, the bank of tubes 6 being spaced from the front and rear casing walls I6 and 26 to provide the customary air flow turning spaces between successive passes. The heated air discharged through the gas outlet opening I! is divided at 22 for flow in parallel through a pair of ducts 21, of substantially equal flow areas and leading, for example, to separate sets of burners in an arrangement such as is shown in the beforementioned patent application, each duct 21 having a damper therein as indicated in the prior disclosure to provide selective control of air flow in accordance with whichever set of burners is being operated.

Air is delivered to the air heater by means of separate forced draft fans 28 and 29 suitably of equal capacities and driven by separately controllable electric motors 3| and 32 respectively,

4 the two fans 28 and 29, when operating simultaneously, providing the maximum rate of air flow required and, by separate operation of either, providing the minimum rate of air flow. The arrangement also enables various intermediate air flow rates to be established utilizing one or more of a variety of known methods such as, speed control of the fan motor, adjustment of fan inlet vanes, and damper control of fan output.

Each of the fans 28 and 29 discharges through a rectangular outlet 34 having its axis 35 of air discharge extending horizontally at an oblique angle to the vertical plane of the air heater air inlet i5, the axes 135, 35 of the two fans being symmetrically arranged with respect to the vertical plane indicated by line l-l, midway between the upright casing end walls 36 and the corresponding ends of the rectangular air inlet opening l5. The inclination of each fan discharge axis 35 to the plane of opening I5 is indicated by angle A which in the form shown is suitably of the order of about thirty degrees, with each axis 35 intersecting that plane at a point intermediate the width of the opening, and the two axes converging at a point 31 within the tube bank 6.

The fans 28 and 29 are each connected to the opening I5 by a discharge duct 38 having vertically disposed opposite side walls 39 and 4| diverging from each other and from the axis of discharge 35 of the associated fan, the angle of divergence between each side wall 4| and an axis 35 being usually greater than the corresponding angle of divergence for each side wall 39. The bottom wall 42 of each duct 38 is horizontal and terminates at the air heater opening 15 substantially on a level with the bottom edge of the opening, in a plane with the transverse baffle l8. The upper wall of each duct 38 includes a wall section 43 sloping upwardly from the fan outlet 34 to provide a duct section 45 of progressively increasing fiow area in the direction of air discharge, an adjoining upper wall section 46 extending horizontally toward the air inlet opening l5 and terminating thereat substantially in a plane with the horizontal upper edge thereof. A damper 41 is included in each upwardly flaring duct section 45 for the purpose of individually controlling the air delivery from each fan' 28 or 29.

The vertical side walls 39 of the horizontally flaring air delivery ducts 38 terminate in end portions 48 which are connected to the ends of the air inlet opening [5, while the opposite vertical side walls 4| meet at an obtuse angle and are connected to each other along a centrally disposed vertical line 49 in advance of the opening, the plane 50 of each side wall intersecting the plane of inlet opening l5 at a location intermediate the width of the opening adjacent the opposite end wall 35, and also intersecting that same end wall 36 between the planeiof theopening and the front tube row 5|, a further extension of each plane 50 intersecting the plane of tube row 51 at a location 52 beyond an end of the row. The side walls 39 are disposed in vertical planes converging at an obtuse angle toward the bank of tubes 6 and intersecting at a location 53, for example, adjacent the rear of the bank, the plane of each side wall 39 intersecting the plane of the front tube row 5| at a location 54 intermediate the width of the row and at a distance from one end of the row within sugsotantially the first one-quarter of the row wi h.

It will be noted that each outer duct wall 39 intersects the plane of inlet openin adjacent an end thereof, and that the planeof each inner duct wall 4! intersects the outer wall '39 of the other duct in the plane of inlet opening [5. Thus, the areas of intersection of ducts 38 with the plane of inletopening l5 are equal and coextensive, so that air is delivered to the inlet opening over a predetermined width thereof irrespective of whether either one or both ducts are carrying air.

The arrangement of two fans 28 and 29, and the horizontally flaring air delivery ducts 38, thus results in distribution of air throughout the entire width of the air heater tube bank between end walls 36, when either or both ducts 38 are operating. Substantially the same extent of distribution is attained irrespective of the rate of air delivery and whether a single fan 28 or 29 is being operated, or both. The distribution of air flow over all of the tubes at the inlet section of the bank, with both ducts operating, is beneficial in that the metal of those tubes is cooled to substantially the same temperature,

thereby resulting not only in equalization of the amount of heat transfer by each tube but also in the maintenance of correspondingly equalized gas temperature conditions within the tubes at the air inlet section zone. Such substantial uniformity of conditions internally and externally of the tubes is beneficial in attaining maximum heat transfer and also in avoiding selective tube plugging and internal tube corrosion. A further operational advantage resulting from the multiple fan and duct arrangement provided accrues from the ability to regulate air flow rate over a wide range. There is also a structural advantage in the arrangement in that the fans and ducts provide a relatively compact assembly closely coupled to the associated air heater.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a co'rresponding use of other features.

I claim:

1. A heat exchanger comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes, and a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, the areas of intersection of the projections of the wall surfaces of each duct with the plane of the inlet opening being equal and coextensive; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts.

2. A heat exchanger comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set offluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; and a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, said ducts having opposing side walls, with the outer wall of each duct intersecting the plane of the inlet opening adjacent one end thereof and the plane of the inner wall of each duct intersecting the outer wall of the other duct substantially in the plane of the inlet opening; whereby fluid is directed into said heater over a predetermined horizontal width ofthe inlet opening irrespective of whether there is fluid flow through one or both of said ducts.

3. A heat exchanger comprising, in combination, a casin enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and thespaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; and a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, said ducts having opposing side walls diverging toward the inlet opening, with the outer wall of each duct intersecting the plane of the inlet opening adjacent one end thereof and the plane of the inner wall of each duct intersecting the outer wall of the other duct substantially in the plane of the inlet opening; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts.

4:. A fluid heater comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conductin passages and the spaces between the tubes defining a separate set of fluid conducting passages-said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rowsof tubes; a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, the areas of intersection of the projections of the wall surfaces of each duct with the plane of the inlet opening being equal and coextensive; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts; and a pair of separate fluid supply means each connected to the outer end of one of said ducts.

5. A fluid heater comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, said ducts having opposing side walls, with the outer wall of each duct intersecting the plane of the inlet opening adjacent one end thereof and the plane of the inner wall of each duct intersecting the outer wall of the other duct substantially in the plane of the inlet opening; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts; and a pair of separate fluid supply means each connected to the outer end of one of said ducts.

6. A fluid heater comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, said ducts having opposing side walls diverging toward the inlet opening, with the outer wall of each duct intersecting the plane of the inlet opening adjacent one end thereof and the plane of the inner wall of each duct intersecting the outer wall of the other duct substantially in the plane of the inlet opening; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts; and a pair of separate fluid supply means each connected to the outer end of one of said ducts.

7. A fluid heater comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, the areas of intersection of the projections of the wall surfaces of each duct with the plane of the inlet opening being equal and coextensive; whereby fluid is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is fluid flow through one or both of said ducts; and a pair of flow regulating means each disposed in one of said ducts.

8. A fluid heater comprising, in combination, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining one set of fluid conducting passages and the spaces between the tubes defining a separate set of fluid conducting passages, said casing having a fluid inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; a pair of fluid inlet ducts each intersecting the inlet opening and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, the areas of intersection of the projections of the wall surfaces of each duct with the plane of the inlet opening being equal and coextensive; whereby fluid is directed into said heater over a predetermined horizontal width oi"; the inlet opening irrespective of whether there is fluid flow through one or both of said ducts; a pair of separate fluid supply means each connected to the outer end of one of said ducts; and a pair of flow regulating means each disposed in one of said ducts.

9. A heater for combustion supporting air comprising, in combinaton, a casing enclosing spaced rows of spaced tubes, the interiors of the tubes defining a set of flue gas conducting passages and the spaces between the tubes defining a separate set of conducting passages for combustion supporting air, said casing having an air inlet opening with a horizontal dimension substantially equal to the width of said rows of tubes; a pair of air inlet ducts each intersecting the inlet open ing and extending horizontally in opposite directions to each other and at acute angles to the plane of the inlet opening, the areas of intersection of the projections of the wall surfaces of each duct'with the plane of the inlet opening being equal and coextensive; whereby air is directed into said heater over a predetermined horizontal width of the inlet opening irrespective of whether there is air flow through one or both of said ducts; a pair of air supply means each connected to the outer end of one of said ducts; and a pair of dampers each regulating the air fiow through one of said ducts.

GEORGE A. TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 559,453 Iles May 5, 1896 2,008,255 Larkin July 16, 1935 2,013,756 Kalischer Sept. 10, 1935 2,066,817 Young Jan. 5, 1937 2,135,461 Wolley Nov. 1, 1938 2,386,188 Artsay Oct. 9, 1945 FOREIGN PATENTS Number Country Date 363,559 Great Britain Dec. 24, 1931 

